Crosshairs (F11) in lightgun games inaccurate?

Pressing F11 in lightgun games brings up a red crosshair for aiming. This crosshair seems well off the actual firing point, in Maze of the Kings for example the gun fires someway up and to the left of the crosshair location.

If I play in windowed mode the gun fires very accurately to the mouse pointer position, this can be verified by checking the hex values on the calibration screen relative to the mouse pointer (eg. pointer top-left = x00).

I want to play in full-screen mode though, where the mouse pointer isn't shown. Is the crosshairs being inaccurate an emulation problem, or can I correct it?

Yes, I tried the service mode gun calibration - the gun is already calibrated to the mouse pointer, but not to the red crosshairs. There's also a calibration test at the start of a new game, where you shoot the bullseye - again the mouse pointer is accurate, but the crosshairs are way off. Maybe a bug?

The problem seems to be that you can't view the red crosshairs during some screens - unfortunately gun calibration being one of those screens! On Confidential Mission the red crosshairs are visible so you can calibrate properly, on House Of The Dead 2, Maze Of The Kings and Lupin III you can't see the crosshairs during gun calibration.